Final answer:
A buffer stop or bumper is placed across the rail to prevent a train from overrunning the end of the track. It absorbs the energy of the train and brings it to a stop, preventing derailing or damage.
Step-by-step explanation:
The device that is placed across the rail to prevent a train from overrunning the end of the track is called a buffer stop or a bumper. A buffer stop is typically made of a large block of concrete or steel, and it is located at the end of the track to absorb the energy of the train and bring it to a stop. It helps prevent the train from derailing or causing damage when it reaches the end of the track.
The buffer stop works by using a combination of friction and deformation. When the train makes contact with the buffer stop, the friction between them generates a force that opposes the motion of the train. Additionally, the buffer stop is designed to deform and absorb the energy of the moving train, helping to bring it to a gradual stop.
For example, at the end of a train track, there may be a buffer stop made of a solid metal block. When a train reaches the end of the track, it will make contact with the buffer stop, and the force of the impact will cause the buffer stop to compress and absorb the energy of the train until it comes to a complete stop.